I understand why people have the "working now, optimized later" attitude. However, this blog post isn't just about making the compiler run faster. It's about getting it to produce faster compiled code. I for one do consider that a feature. It's also something that would likely be harder to rough in later in the project. A working spec-complete compiler that does basic optimization from the start is more likely, I think, to be used than one that is spec complete and produces very slow programs.